Xerographic apparatus and method



Jan. 17, 1961 R. w. GUNDLACH 2,968,552

I XEROGRAPHIC APPARATUS AND METHOD Filed Oct. 1, 1956 3 Sheets-Sheet 1 HIGH 9 3 VOLTAGE 22 L l SOURCE 21 I INVEN TOR.

' ROBERT W. GUNDLACH AH'URFEY Jan. 17, 1961 R. w. GUNDLACH 2,963,552

XEROGRAPHIC APPARATUS AND METHOD Filed Oct. 1, 1956 3 Sheets-Sheet 2 INVEN TOR. ROBERT W. GUNDLACH Armin? Jan. 17, 1961 R. w. GUNDLACH 2,958,552

XEROGRAPHIC APPARATUS AND METHOD Filed Oct. 1, 1956 s Sheets-Sheet s IN V EN TOR. ROBE RT W GUNDLAC H ATTORNEY Patented Jan. 17, 1961 tially infinite overexposure without significant image impairment.

According to one embodiment of the present invention ,9 a transferable deposit of charged, finely divided material 5 is placed on a suitable surface such as, for example, a XEROGRAPHIC APPARATUS AND METHOD photoconductive insulating surface, and is transferred Robert W. Gundlach, Spencerport, N.Y., assignor to from said surface to an adjacent print-receiving surface Haloid Xerox Inc., a corporation of New York under the influence of changing electrical fields such as is caused by a flow of current which may, for example, Flled 1956 be as a result of exposure of the photoconductor to a 17 Claims. (Cl. 96-1) pattern of light and shadow to be reproduced. The method and apparatus are illustrated in the following drawings in which:

Fig. 1 is a diagrammatic flow sheet of the operation of This invention relates in general to the formation of the invention according t one speelfie embodiment;

developed electric images and in particular to the simul g- 2 is a Xefogrephio machine according to one taneous formation and development of electric images bodiment of the invention, including an g l l gh as, for example, in response to the action of light. sensitive member;

This application is a continuation-in-part of my cog- 3 is a Xel'ogfaphio mnehine aeeofdlng to anoihel' pending application Serial Number 505,963, filed May 4, 20 embodiment of the invention, adapted to employ a photo- 1955, now Patent No. 2,901,374, issued on August 25, conductor separately mounted on the m h 1959, One method of operation of the present invention is In the art of Xerography as exemplified b C l illustrated in Fig. 1 wherein are shown a series of steps United States Patent 2,297,691, and related patents, it is and p o u according to which a v e image is usual to form an electrostatic or xerographic latent image formed-1n direct po to an n e of hght and Shadow which is subsequently utilized optionally through the to be l'eeofded- A5 Illustrated in 1 a p p deposition thereon of charged, finely divided material. SiVe membe1' gene1any de5ignaied y comprise a The sequence of operations in such conventional xerophotoeondnetlye lnsnlnhng y 11 p e on a graphic art comprises first charging a photoconductive dnetlve pp generally deslgnnted 12 Whleh y. for

insulating layer or otherwise applying a field therethrough eXemPIe, co'mPTiSe condnotive coating of layer 13 on followed by exposing the charged layer to a light image iranspnlent backing Support Innstrahveiy. the

to form the xerographic latent image. This image may backing pp y be y transparent member Such then be made visible by deposition of charged material as, p glass, transparent plastic of him of y su h a fo x le, charged o d or it may b h desired sort either inherently conductive or having a wise utilized f l to generate an 1 i conductive coating on at least one surface thereof. For signal or to control electric discharge. In the normal p Partially silvered of nleiahled glass y he course of operation the image is developed and is then p y as the haeklng pp of glass With other fixed in place either on the photoconductive layer, in dnotive eoatings- A Presently Preferred base pp is which case the light-sensitive material becomes a con- NESA glass which is understood to he glass having sumable item, or the image is first transferred to a print- 40 conductive tin oxide Coating on its f available f receiving surface and fixed in place on said surface, in Plttsbnlgh Plate Glass Company, Pittsburgh, y

which case the photosensitive layer can be cleaned of Vanlaresidual powder and is reusable. The exposure to light The Photoeonductol 11 InElly be y Suitable P or other image source is, as in other photographic opera- Fonduenve layer h as, for p a Photoeondnetive tions, controlled to give an optimum exposure level to ns ator conventional to the xerographic art. Such form an image of proper density, contrast, em photo-conductive insulators include vitreous or amor- Now, in accordance with the present invention there is PhonS Selenlnnl deposlted by Vacuum deposition, p yprovided a new art for the formation and development or melt-Coating ethod to form a photoconductive of electric images in which the electrical image is siinsulating layer on the support surface. In a t multaneously created and developed. It is accordingly there may be employed other photoconductors such as an object of the present invention to provide new means, anthracene, sulfur, or hinder layers of photoactive mamethods, and apparatus for the simultaneous formation terials such as certain sulfides, oxides and selenides of and development of electric images. zinc, cadmium, calcium, lead and other elements. A It is another object of the invention to provide new suitable material of this sort may be a photoconductive means, methods, and apparatus for the simultaneous forinsulating layer comprising a photoactive material such mation and development of an electrical image through as, for example, zinc oxide in a film-forming binder such changing electric fields in response to a light image or as, for example, an insulating silicone resin or the like. pattern of light and shadow to be recorded. As illustrated in Step 1 of Fig. 1, a layer 16 of powder It is an additional object of the invention to provide or similar transferable finely divided material is deposited a simplified means, methods, and apparatus for the for- 6 on the surface of the photoactive member as, for exmation of a developed electrical image in response to a ample, by deposition from a rotating brush 17. This pattern of light and shadow to be recorded wherein one material is deposited in a form such that it adheres loosely or more of the steps of conventional xerographic operato the plate surface by mild electrostatic forces or simition are eliminated. lar attractive forces. This can be accomplished by dep- It is a specific object of the invention to provide new osition of a suitable material as is conventional in the means, methods, and apparatus for the formation of a xerographic developing art. Such deposition may be acxerographic image on a surface adjacent to a reusable complished as illustrated in Fig. 1 by deposition from photoconductor while avoiding cleaning operations for a rotating brush or by deposition from a mixture of fine the reuse of such photoconductor. particles with larger size carrier particles as illustrated It is a further object of the invention to provide a for xerographic development in Wise Patent 2,618,552. new xerographic means, methods, and apparatus having The developer material or powder may, in addition, be

an extremely wide exposure latitude permitting substandeposited by a dusting or spray deposition method such as employed in the previously mentioned Carlson patent for the development of xerographic images. Other deposition methods may be employed as desired to deposit on the plate surface a thin film orcoating' of loosely attracted, electrically transferable material. As illustrated in Step 1, the powder is being deposited on the plate surface by a rotating powder-laden brush moving from left to right across the plate surface, the brush being triboelectrically positive with respect to the powder so as to deposit negatively charged particles or" powder on the plate surface. 7

In Step 2 of Fig. 1 an appropriate electric charge is placed on the deposited powder, for example, by passing a corona discharge electrode 19 across the'plate surface. A suitable corona discharge electrode is disclosed in copending application Serial Number 154,295 by Lewis E. Walkup and may comprise one or more fine conductive strands 20 maintained at a corona discharge potential by high voltage source 21 and positioned within a backing shield 22 and optionally additionally shielded or screened by an array of conductors between the corona discharge wires and the surface being charged. The fine conductive wires are maintained at a desired corona discharge potential such as, for example, a potential in the order of several thousand volts and may be controlled to deposit on the surface electric charge of the desired polarity. As illustrated in Step 2, the corona discharge is being moved across the plate surface from left to right to deposit negative polarity charge on the developer powder previously deposited on the plate surface. In this step or operation an electric charge of the desired polarity is placed on the layer of powder or developer material, in the event that said layer does not already possess electric charge of the desired polarity.

In Step 3 is illustrated the simultaneous exposure and development according to one embodiment of the present invention. In this operation a suitable print-receiving pellicle, such as, for exampe, a sheet or web of paper 23 or the like, is placed against the dusted and charged plate surface and is held against it with mild pressure. While the print-receiving surface is positioned against the active surface of the plate, the photoconductor 11 is exposed to a pattern of light and shadow to be reproduced, for example, by projecting the image through the transparent backing support member 12. As a result of this exposure operation, the transferable developer material in the dark or unexposed areas is transferred to the printreceiving surface, and is removed on the print surface when said surface issubsequently or simultaneously re-. moved from the photosensitive surface.

It is presently believed that the development transfer of the transferable developer material is brought about by changing fields of force operating on charged particles during the exposure operation as illustrated by the positions of plus and minus signs in the drawing at Step 3, with the uniform charge on the transferable powder layer performing the dual functions of providing the initial force for bringing about these changing fields and simultaneously causing transfer of the layer as a result of the changing fields. In effect, this is as if the image is developed as the result of flow of electric current rather than formation of an electric image. Prior to the exposure operation conditions of uniform field exist with the transferable developer material being charged to a substantially uniform potential of the desired (in this case negative) polarity. Positioned against this charged powder layer is the print-receiving surface 23 which may, desirably, be at least mildly conductive so as to present an equipotential surface adjacent to the charged developed layer. As the exposure to the light image is in progress, the charge on the developer layer is partially and selectively balanced by the migration of charge of opposite polarity through the photoconductive layer.

Thus, charges of opposite or neutralizing polarity migrate into substantially closer proximity to the charged transferable developer material in the areas wherein conductivity is induced by the action of activating radiation. In the dark or unexposed areas, such reduction of potential does not occur. There is, however, in the event of conductivity in print-support member 23, lateral migration of charge to maintain an equipotential surface and also, if the member 23 be grounded, a net flow of neutralizing charge from ground, resulting in varying electrical field between the powder and this equipotential surface depending on the degree to which the charge on the developer layer has been partially balanced by the penetration of charge in the photoconductive layer. The net result is that the print-support member receives, in the dark areas, a concentration of charge of polarity opposite to the developer layer. In the dark or unexposed areas there has thus been produced an electric field from the photoconductor layer to the print-receiving surface in a direction to promote migration or transfer of this transferable developer material from the plate surface to the print-support surface. In the light or exposed areas, the transferable material is conversely more strongly attracted to the now closely-adjacent neutralizing charge at the surface of the photoconductive layer, thus preventing transfer in these areas. Whether this theory of operation be in fact correct, it is, nevertheless, true that transfer of the developer material occurs with the result that a developed image is formed on the print support surface to provide a useful visible image on the print.- support surface. This print-support surface may then be removed from the photosensitive member with the image deposited thereon and utilized as desired. Optionally, it may, for example, be placed in an atmosphere of a vapor which is a solvent for the support surface or for the deposited material, or may be heated or otherwise treated so as to fuse either the deposited developer material or the support surface itself to form a permanent image. If desired, the image may be otherwise utilized by transfer to a different surface or by other uses or applications of such an image.

In Step 4 is illustrated one method of preparing the photosensitive member for recycling through the imag forming steps of the present invention, whereby reproducibility of charge conditions is assured for successive cycles. In this operation a corona discharge electrode 24 is passed across the plate surface, preferably after the print-support surface has been removed, and the plate is preferably exposed to light across its entire area. In this reparation step any electrical charges residing on the residual layer after transfer of the developer material, as well as electrical charges in or on the photoconductive layer, are effectively neutralized to bring the developer and photoconductor combination to a suitable condition of reproducible electric charge and potential from which condition the cycle of operations can be repeated. In the operation as illustrated in Step 4, corona discharge electrode 24 is of polarity opposite to the polarity of the electrode 19 of Step 2 and may, for example, deposit a charge of positive polarity. This electrode 24 may optionally be the same electrode as electrode 19 connected through a suitable reversing switch (not shown) to provide opposite polarity, or it may be a separate electrode appropriately connected to an opposite polarity high voltage source 21tz. As a result of the deposit of such charge combined with exposure of the photoconductive layer to light as, for example, by flooding light through the transparent support surface, any residual charge within or at the surface of the photoconductive layer as may have been induced therein or thereto by the prior sequence of steps is now neutralized. The plate is then ready for recycling through the sequence of operations, beginning again with the operation of Step 1.

The general nature of one embodiment of the invention having been] set forth, the following examples are, now presented in illustration. but not limitation of a method, apparatus, and procedure for the production of one or a sequence of developed images in response to the action of light.

Example I A photosensitive plate for operation in accordance with this invention was prepared by coating vitreous selenium onto a transparent conductive glass base plate. The base plate was a conductively coated glass plate available under the name NESA glass and believed to be a glass support surface having a thin conductive tin oxide coating on its surface. For the coating operation the glass was placed in an evaporation chamber and the pressure was reduced to about one-half micron of mercury. Thereupon selenium was evaporated onto the glass surface while the glass was maintained at a temperature of about 60 C. The evaporation was continued to form a SO-micron selenium layer. The plate, after coating, was found to have an insulating selenium layer on its surface which layer became conductive upon exposure to light.

The thus prepared photosensitive plate was preliminarily dusted by cascading across its surface a powder carrier mixture such as is disclosed in Walkup U.S. Patent 2,618,551. The mixture employed was based on a xerographic developer under the name XeroX Long Life Developer, Type available from The Haloid Company, Rochester, New York, with supplemental xerographic toner added to bring the toner composition to about 4% by weight. The toner employed was XcroX Long Life Toner, Type 10, also available from The Haloid Company, Rochester, New York, and consisted of finely divided, pigmented particles of a thermoplastic resin. The toner developer mixture is characterized by containing negatively charged toner or powder particles mixed with grossly larger carrier particles.

The developer mixture was cascaded back and forth across the selenium surface until there was deposited on the selenium a uniform layer of the powder. Desirably, the powder layer is sufficiently thick so as to hide the selenium surface, and is at least thick enough so as to substantially completely eliminate specular reflection from the plate surface. The plate was then started in a series of cyclical operations, the first of which comprised charging the plate surface positively, and either simultaneously or subsequently exposing the plate to light through its transparent backing. For the charging operation there was employed the charging mechanism of commercial xerographic equipment available under the name XeroX Processor, Model D. The charging equipment was adjusted to give a bare plate current of 29 microamperes and charging was accomplished by moving the charging electrode across the plate surface at a rate of 2.4 inches per second for a total of two passes of the electrode across the plate surface. After exposure to light the plate was then charged negatively in the absence of illumination and wasagain dusted by cascading the developer mixture across the plate surface. It was again charged negatively after which it was placed in the exposure position. After exposure, as hereinafter described, the plate was repeatedly cycled through the operations beginning with the positive charging step.

In the exposure operation the plate was positioned with its glass backing member toward the desired image light source. A sheet of ordinary typewriter paper was placed against the dusted surface and manually held against the surface at a firm but relatively light pressure. To secure the desired uniform light pressure and to insure electrical conductivity in and behind the paper a half-inch thick pad of foam rubber previously impregnated with a graphite suspension was placed on a stiff fiat surface and this pad was then pressed manually against the sheet of paper. The foam rubber pad was grounded through the hands and body of the operator. The plate was then exposed to a projected image of copy to be reproduced for an optimum exposure time which in the particular apparatus employed was about 30 secondsv At the end of this time the paper was removed from the dusted plate surface and carried with it a powder image corresponding to the image projected onto the plate. The original subject matter consisted of printed black characters and lines on a white background and the copy produced was a mirror image copy of the same printed black characters and lines on the white typewriter paper. In duplicate procedures using an optical reversing system, right-reading copy was formed.

The procedure as described was repeated under control test conditions through ten cycles to produce uniformly good copy reproducibly from one cycle to another. In addition, under varying operating and test conditions it was repeated for a multitude of cycles over a period of months, again uniformly producing good copy. I

The copy as produced comprises a visible powder image on a sheet of paper. This may be used as desired such as, for example, by fusing through exposure to heat and/or solvent vapor, or through transfer to other surfaces or in other uses and applications as desired.

Example 11 The procedure of Example I was repeated with numerous variations and modifications in procedure for preparing the dusted plate. In one modification, the photosensitive plate was charged positively and dusted as described in Example I. The powder layer was then again charged positively and the plate was placed in the exposure position and exposed as in Example I.

in another sequence of operations, the plate was charged positively and dusted as in Example I, after which the powder surface was negatively charged and the plate placed in an exposure position.

In another sequence the plate was first charged positively and exposed to room light and then charged negatively and exposed to room light, after which it was dusted and in the dark again charged negatively before exposure.

In another sequence of operations the plate was positively charged and exposed to light, positively charged in the absence of light, dusted, and negatively charged after which it was placed in the exposure position.

In each of the above sequences, the identical procedure was carried on through ten cycles of dusting, charging, and exposing.

In another sequence, the plate was charged negatively and exposed to room light, after which it was dusted and again charged negatively. It was again placed in the exposure position. After exposure and transfer of image powder to the image-receiving sheet, the plate was charged positively and exposed to room light, and again dusted and charged positively in the absence of illumination. It was then placed in the camera for exposure. The entire cycle of alternate negative and positive charging operations including exposure and image formation was repeated for ten double or positive and negative cycles.

In all of the operations as described, a black character in line image on white background was formed when the plate, charged and dusted as described, was exposed to an image while a sheet of paper was in light contact with the dusted surface. In all of the cases, the cycles were repeated ten times to establish continuity and reproducibility. In some of the cases, image intensity gradually decreased and it is believed that this decrease in intensity was caused by progressive balancing of charge on the powder with a built-up induced charge at the selenium surface. It was found in general that a step of charging the powder surface and flooding with light between cycles caused a reproducible charge condition to be achieved between cycles such that subsequent charging operations produced equivalent and reproducible results.

Example III The plate prepared, dusted, and charged, as in Example I was employed for the formation of an image on a variety of test surfaces under modified conditions of operation. In one case the plate was exposed in a horizontal position with its dusted side up and a piece of paper laid loosely on top of the plate at a pressure caused solely by the weight of the paper. Image formation in areas of contact was found to be satisfactory but non-uniformity of contact was apparent through spotty areas in which absence of contact was indicated by absence of image formation. In a subsequent operation, the plate was charged and exposed as in Example 1, except that the dusted plate surface was not in contact with an image transfer sheet, but instead was exposed to the open air in the absence of ambient light. in one case a sheet of paper was subsequently pressed flat against the surface after exposure and in another case the sheet of paper was rolled against the surface after exposure. In each case an image was formed on the paper by contact with the charged, dusted, and exposed surface.

In separate test procedures, the procedure of Example I was repeated in one case employing ordinary typewriter paper which had been exposed to ambient room humidity conditions for a period of at least minutes, and in the other case employing a sheet of the same paper that had been oven dried immediately prior to exposure. In each case there was formed an image copy of the lines and characters of the original. In the ca e of the paper allowed to remain at ambient room humidity conditions prior to use. the image was more dense and dark in lar e black areas than in the case of the paper which had been dried prior to use. It is presentlv believed that the difference was due to lateral conductivity in the paper at ambient room humidity conditions as distinguished from the substantially insulating character of the dried pa er.

In another sheet of test operations, ordinary and specially dried papers as described were employed, first, while being pressed against the sur ace by an insulating foam rubber pad, and, second while being pressed against the surface with such a pad having an intermediate sheet of electrically conductive padding between the pad and the image-receiving sheet. and, third, while having a sheet of aluminum foil between the foam rubber pad and the image-receiving sheet. In all cases where an electrically conductive surface was present in or behind the imagereceiving sheet there was improved density of image in larger dark areas.

In another procedure, the procedure of Example I was repeated employing a sheet of aluminum foil as the image-receiving surface. In a comparable procedure a sheet of insulating plastic film was employed as the image-receiving surface the film being a polyester film available under the name Mylar. In each case an image was formed on the receiving surface with the difference that the image on the aluminum foil was more dense and particularly more dense in large dark areas.

The procedure of Example I was repeated using as the original a mirror image negative photocopy characterized by having white characters and lines on a black background. During exposure an electrical potential of 100 volts was applied between the conductive glass surface and a sheet of aluminum foil positioned behind the image-receiving sheet of paper. The aluminum foil was maintained positive with respect to the conductive glass surface. A dense black copy of the original was formed.

Example IV The procedure of Example I was repeated under optimum exposure conditions. The optimum exposure for the plate in question was determined by cycling the plate through conventional xerographic steps of charging its surface to positive polarity, exposing to the test image, and developing by cascading across its surface XeroX Long Life Toner, Type 10. After optimum exposure had been established, the procedure of Example I was repeated at optimum exposure levelwhich in this apparatus was 30 secondsone-half optimum exposure, onefourth optimum exposure, and one-eighth optimum exposure. In addition, exposure was repeated at 2 times, 4 times, 8 times, 16 times, and 32 times optimum exposure. For purposes of comparison, exposure and development were repeated for standard xerographic operations at the same exposure levels. According to the procedures of the present invention, an image was formed with an exposure of one-fourth the optimum exposure level and was made considerably more dense at one-half optimum exposure level. A relatively dense black image was formed at optimum exposure conditions and images of substantially unimpaired quality and density were formed at all exposure levels greater than optimum exposure. By contrast, in the case of conventional xero graphic operation, highly satisfactory images were formed in the range from one-half to about three or four times the optimum exposure level, but when exposure was continued above about four times image quality deteriorated badly. At an exposure level of 8 times optimum, the image was almost completely washed out. No image was detectible by conventional methods at an exposure greater than about eight times the optimum expo-sure level.

In Fig. 2 is illustrated a machine for intermittent or sheet-feed operation to produce copies of letters, documents, and the like, according to the present invention. Generally illustrated within a light-tight cabinet 29 is a xer-ographic cylinder 39 comprising a conductively coated support cylinder such as, for example, a cylinder of NESA glass, or the like. In an image area comprising a segment of the cylinder surface, the xerographic cylinder is coated with a photoconductive insulating layer 31 such as a layer of selenium or the like, and in the remainder of the surface area the cylinder is substantially transparent. The cylinder is suitably rotatably mounted and provided with drive means such as, for example, an electric motor or the like, or, optionally, manual drive mechanism to cause the cylinder to be rotated.

Positioned at an appropriate point around the circumference of the xerographic cylinder is an exposure station 32. There may be, for example, suitable lighting means such as fluorescent tubes 33 mounted within the cylinder at the exposure station. Light shields are positioned to protect the photosensitive portion of the drum from undesired exposure to the light of the exposure light source.

Mounted outside the cylinder 3% at the exposure station is a roller 36 adapted to be moved in and out of position in contact with the xerographic drum surface. Preferably, suitable cam 37, operating through rocker arm 38, moves the roller 36 into contact with the drum through 180 of rotation so as to bring the roller into contact only at those points which are not coated with the photoconductor.

Mounted Within the cylinder is a suitable optical system adapted to focus a split projection image of the original onto the opposite surface of the cylinder at a position removed from the exposure zone by 180. This optical system may, for example, comprise a roof mirror or prism 39, a reversing mirror 4i), and a lens 43. so aimed and adjusted as to project and focus the image at the desired point. An original 4-2 to be copied may be fed between the cylinder and the drum and is carried through the exposure station by the rotating cylinder and roller in co-action. Suitable paper feed means 43 is operably positioned to feed the sheets of the original into roller as and cylinder 30.

Positioned adjacent the circumference at a point 180 from the exposure station is an image formation station generally designated 44. At this station is a suitable roller 45 having a soft, resilient surface such as, for example, a thick sponge rubber layer 46 which desirably is electrically conductive. Conductivity may be imparted to otherwise nonconductive rubber by impregnation with a conductive material such as, for example, a graphite dispersion. A suitable cam and rocker arm combination is is positioned and adapted to move roller 45 into and out of contact with the xerographic cylinder essentially simultaneously with roller 36. A suitable copy paper 47 is adapted to be fed between the sponge rubber roller 45 and the xerographic cylinder and to be carried through simultaneously with and in reverse direction from the original being copied. The copy paper may, as desired, be sheet fed or may, as illustrated be web fed from feed roll 49 to take up roll 50. An exposure frame or slit 51 is defined by shield edges 52 and 53, these edges being adjustable in position so as to control the width of the exposure slit opening. Thus, as the original is being fed against the surface of the xerographic cylinder at one point, an image thereof is being focused onto the opposite surface of the cylinder through the optical system and slit at a position 180 removed from the original.

Mounted between the exposure and image formation stations and shielded from both the exposure light source and the projected image is an operational charging station 54. At this charging station is positioned suitable charging means such as, for example, a corona discharge electrode 55 of the type described in conjunction with Figure 1. This corona electrode is connected to a first polarity voltage source such as the negative terminal of a suitable high voltage power supply source, as shown in Fig. l, and is adapted to deposit negative polarity electric charge on the surface of the photoconductor.

Optionally on the opposite side of the image formation station and subsequently thereto in the direction of rotation of the cylinder is an opposite charging electrode such as, for example, a corona discharge electrode 57 connected to the opposite or positive polarity terminal of a power supply as for example the power supply 21a of Fig. l. Cooperatively mounted within the cylinder at the same point in the path of rotation, or at a subsequent point, is a flood light source such as, for example, a fluorescent tube 58 mounted within a light shield 59 being positioned and adapted to shine light through the xerographic cylinder onto the photoconductive insulating layer.

Positioned next adjacent to this opposite charging electrode 57 is a developer supply means 61 comprising, for example, a rotatable brush 62 bearing a supply of finely divided developer material optionally maintained in supply by brushing against a developer-feed hopper 63 which is adapted to supply additional developer material thereto. The brush is movably mounted to be brought into and out of contact with the rotating cylinder with suitable cam and rocker arm 61 adapted to move the brush into contact only with the photoconductor coated portion of the cylinder.

in use and operation, the machine of Figure 2 is adapted to produce copies of suitable sheet-by-sheet originals. The desired original is fed between roller 36 and cylinder 30, and simultaneously appropriate copy paper is fed between rollers 45 and cylinders 30. As these rollers are moved by the cam into contact with the cylinder, they draw the original and the copy paper simultaneously through the exposure and image formation station at identical rates of speed. While the two are being drawn through the machine, the light image of the original is being focused through slit 51 and through the transparent conductive support of the cylinder onto the photoconductive layer. Thus, at the image formation station a developed visible image is placed on the copy paper in accordance with Example I. The copy paper is then passed through suitable fixing apparatus such as, for

example, a solvent vapor chamber of a heating oven 64 including heat sources such as heat lamps 65 or the like. By operation of this machine the series of operations illus trated in Fig. l are sequentially repeated on the photo conductor layer. Thus, Step 1, or deposition, is carried out by the developer deposition means 61, followed by Step 2, or operational charging, by charging electrode 55. Next, Step 3 is carried out simultaneously at the exposure station and the image formation station, whereby copy paper is fed to the image formation station and a light image is produced by feeding the original at the exposure station. Finally, Step 4 is produced by reverse charging electrode 57 in conjunction with the lamp 58.

In Fig. 3 a machine generally similar in purpose and function with the machine of Fig. 2 is adapted to produce continuous copy from a web 7 of prepared photosensitive material. In this device a transparent cylinder 72 such as, for example, a cylinder of. NESA glass is suitably, rotatably mounted in a light-tight cabinet 29 and adapted to be driven at constant speed by a drive motor or the like (not shown). Mounted within the cylinder is an optical system including a roof mirror or prism 3S, reflecting mirror 40, and lens 41, as in Fig. 3. Positioned at the exposure station are light sources such as lamps 33 within shields 34, again as in Fig. 2. A copy feed roller 36 is mounted, for example, at the base of the cylinder to feed through the exposure station a suitable original subject 42.

Positioned opposite the exposure station is an image formation and transfer station including roller 45 having a soft resilient coating 46 such as a sponge rubber coating preferably electrically conductive. A prepared photoconductor web 71 is supplied from a feed roller 73 and is positioned to move past an operational charging electrode 55 between roller 45 and the cylinder and to a suitable take-up roll 74. Positioned and adapted to feed between the web 71 and the roller 45 is a web of copy paper 75 passing from feed roll 76 to take-up roll '77. Permanent fixing of the image is accomplished by a suitable fusing means such as a vapor chamber 79 loaded, for example, with a volatile, solvent-impregnated, absorb ent filler it such as cotton batting or the like.

The web 71 of prepared photosensitive material may comprise any suitable photoconductive insulating layer. This layer, if not self-supporting, may desirably be supported on a transparent film or pellicle such as, for example, a web of any available plastic such as, for example, Mylar, cellulose acetate, other cellulosic derivatives, polystyrene, polyethylene, Teflon, or the like. The support film may be an electrical conductor or, if thin, may be an insulator. If desired, a suitable fibrous support base preferably treated so as to make the fibrous materials substantially transparent, may be employed, and if image quality is not significant, a conventional, fibrous, paper support base may be used. A suitable photoconductor may, for example, be a pigment binder composition such as described in connection with Figure 1.

In preparation for operation with the machine, the photoconductor layer has been previously dusted in accordance with step 1 of Figure l to place on the photoconductor surface a layer of loosely adhering, transferable developer material.

In use and operation the original to be copied is fed between roller 38 and cylinder 72 at the exposure station, and the photoconductor and copy paper are simultaneously fed between roller 45 and the cylinder. The dusted surface is positioned away from the cylinder 72 and in contact with the copy paper 75. Prior to entering the transfer and image formation station the dusted surface of the photoconductor receives an operational charge from electrode 55. In this manner, the projection of the light image of the original through the trans parent cylinder onto the dusted and charged photoconductor causes formation of the developed image on the 11 copy paper. The result is a reproduction of the original which may be utilized as desired, such as, for example, by fixing to form a permanent print.

It is to be understood that variations and modifications in procedure and apparatus may be made within the scope of the invention. For example, the invention has been described with reference to document copying, and it is to be understood that it is of general application to the reproduction or copying of any photographic image, including three-dimensional objects, scenes, and the like. Similarly, it is to be recognized that the photoconductors described in the specification are sensitive to light other than light in the visible spectrum, including infrared and ultraviolet light as well as, in many cases, X-rays and similar penetrating radiation. It is apparent, therefore, that the present invention may be applied to recording of X-ray and other penetrating radiation patterns in which case the transparent backing support 14 may be a support transparent to such penetrating radiation. In other words, for many applications it is possible to employ metal support surfaces as transparent bodies. These and other variations and modifications will be obvious to those skilled in the art and can be made without departing from the scope of the invention.

What is claimed is:

l. The method of forming a xerographic print on a transfer member comprising forming a uniformly electrostatic charged layer of developer powder on the surface of a photoconductive insulating layer, then exposing the photoconductive insulating layer to an image pattern of light and shadow to be reproduced and plac ing the transfer member in contact with the charged developer powder to transfer a powder image to said transfer member, said transfer member being characterized by its ability to laterally conduct electricity.

2. The method of claim 1 in which said transfer member is placed in contact with said powder layer prior to exposing said photoconductive insulating layer to said image pattern.

3. The method of claim 1 in which said transfer member is placed in contact with said powder layer after exposure of said photoconductive insulating layer to said image pattern.

4. The method of claim 1 in which said transfer member comprises paper.

5. The method of claim 1 in which said uniformly electrostatically charged layer of developer powder is formed on the photoconductive insulating layer by first depositing a substantially uniform layer of developer powder on the surface of the photoconductive insulating layer, and then by depositing a uniform electrostatic charge on said layer of developer powder.

6. The method of forming a xerographic print comprising depositing a substantially uniform layer of insulating developer powder on the surface of a photoconductive insulating layer, said photoconductive insulating layer overlying a transparent backing member, uniformly charging said layer of developer powder by depositing a uniform electrostatic charge thereon, subsequently exposing the photoconductive insulating layer to an image pattern of light and shadow to be reproduced directed to said photoconductive insulating layer through said transparent backing and placing a transfer member in contact with the charged developer powder layer to transfer a powder image to said transfer member, said transfer member being characterized by its ability to laterally conduct electricity, and separating said transfer member from said powder layer carrying a particle image conforming in configuration to the shadow areas of said image pattern.

7. The method of forming a xerographic print comprising depositing a substantially uniform layer of insulating developer powder on the surface of a photoconductive insulating layer, said photoconductive insulating layer overlying a transparent backing member, uniformly charging said layer of developer powder by depositing a uniform electrostatic charge thereon, subsequently exposing the photoconductive insulating layer to an image pattern of light and shadow to be reproduced directed to said photoconductive insulating layer through said transparent backing and placing a transfer member in contact with the charged developer powder layer to transfer a powder image to said transfer member, said transfer member being characterized by its ability to laterally conduct electricity, applying to said transfer member a bias potential, and separating said transfer member from said powder layer carrying a transferred particle image conforming in configuration to the light and shadow pattern to which said photoconductive insulating layer was exposed.

8. The method of claim 7 in which the bias potential is about volts and in which a dense image conforming in configuration to the shadow areas of the light and shadow pattern is produced on the transfer member.

9. The method of forming a xerographic print on a transfer member comprising forming a uniformly electrostatically charged layer of developer powder on the surface of a photoconductive insulating layer, then exposing the photoconductive insulating layer to an image pattern of light and shadow to be reproduced and placing a first surface of a thin sheet-like insulating transfer member in contact with the charged developer powder layer to transfer a powder image to said transfer member, said second surface of said transfer member opposite to said first surface of said transfer member having a conductive electrode positioned thereat.

10. The method of claim 9 in which said transfer member is placed in contact with said powder layer prior to exposing said photoconductive insulating layer to said image pattern.

11. The method of claim 9 in which said transfer member is placed in contact with said powder layer after exposure of said photoconductive insulating layer to said image pattern.

12. The method of claim 9 in which said uniformly electrostatically charged layer of developer powder is formed on the photoconductive insulating layer by first depositing a substantially uniform layer of developer powder on the surface of the photoconductive insulating layer, and then by depositing a uniform electrostatic charge on said layer of developer powder.

13. The method of forming a xerographic print comprising depositing a substantially uniform layer of insulating developer powder on the surface of a photoconductive insulating layer, said photoconductive insulating layer overlying a transparent backing member, uniformly charging said layer of developer powder by depositing a uniform electrostatic charge thereon, subsequently exposing the photoconductive insulating layer to an image pattern of light and shadow to be reproduced directed to said photoconductive insulating layer through said transparent backing and placing a first surface of a sheet-like insulating transfer member in contact with the charged developer powder layer and a conductive member in contact with the second surface of said transfer member opposite to said first surface to transfer a powder image to said transfer member, and separating said transfer member from said powder layer carrying a particle image conforming in configuration to the shadow areas of said image pattern.

14. The method of forming a xerographic print comprising depositing a substantially uniform layer of insulating developer powder on the surface of a photoconductive insulating layer, said photoconductive insulating layer overlying a transparent backing member, uniformly charging said layer of developer powder by depositing a uniform electrostatic charge thereon, subsequently exposingv the photoconductive insulating layer to an image pattern of light and shadow to be reproduced directed to aoeasua said photoconductive insulating layer through said transparent backing and placing a first surface of a sheet-like insulating transfer member in contact with the charged developer powder layer, placing a conductive member in contact with the second surface of said transfer member opposite to said first surface, applying to said conductive member a bias potential to transfer a powder image to said transfer member, and separating said transfer member from said powder layer carrying a particle image conforming in configuration to the light and shadow pattern to which said photoconductive insulating layer was exposed.

15. The method of claim 14 in which the bias potential is about 100 volts and in which a dense image conforming in configuration to the shadow areas of the light and shadow pattern is produced on the transfer member.

16. Xerographic apparatus comprising a xerographic plate comprising a photoconductive insulating layer overlying a transparent backing member, a plate loading station to deposit a uniform layer of developer powder across the surface of said photoconductive insulating layer of said plate, a charging station adapted to uniformly charge a deposited layer of powder on said plate, an exposure and transfer station adapted to transmit a light and shadow pattern of an image to be reproduced through said transparent backing member and to said photoconductive insulating layer of said plate and adapted to feed a transfer web toward the opposite surface of said plate and into contact with the powder layer on said plate and including an electrode positioned and disposed at the surface of the transfer web opposite the surface of the web fed into contact with the powder layer, and means to move said plate in only the following sequence first through said plate loading station next through said charging station and next through said exposure and transfer station to form a print on the surface of the transfer web which contacts the powder layer of the light and shadow pattern transmitted to said plate at said exposure station. 1

17. Xerographic apparatus comprising a xerographie piate comprising a photoconductive insulating layer overlying a transparent backing member, a plate loading station to deposit a uniform layer of insulating developer powder across the surface of said photoconductive in sulating layer of said plate, a charging station adapted to uniformly charge a deposited layer of powder on said plate, an exposure and transfer station adapted to transmit a light and shadow pattern of an image to be reproduced through said transparent backing member and to said photoconductive insulating layer of said plate and adapted to feed a transfer web toward the opposite surface of said plate and into contact with the powder layer on said plate and including an electrode positioned and disposed at the surface of the transfer web opposite the surface of the web in contact with the powder layer, web separating means to remove the web from the exposure and transfer station, and means to move said plate in only the following sequence first through said plate loading station next through said charging station next through said exposure and transfer station and next to said web separating means to form a print on the surface of the transfer web which contacts the powder layer of the shadow areas of the light and shadow pattern transmitted to said plate at said exposure station.

References Cited in the file of this patent UNITED STATES PATENTS 2,573,881 Walkup et a1. Nov. 6, 1951 2,752,833 Jacob July 3, 1956 2,756,676 Steinhilper July 31, 1956 2,758,524 Sugarman Aug. 14, 1956 2,758,525 Yeates Aug. 14, 1956 2,758,939 Sugarman Aug. 14, 1956 2,808,328 Jacob Oct. 1, 1957 2,817,598 Hayford et al Dec. 24, 1957 

1. THE METHOD OF FORMING A XEROGRAPHIC PRINT ON A TRANSFER MEMBER COMPRISING FORMING A UNIFORMLY ELECTROSTATIC CHARGED LAYER OF DEVELOPER POWDER ON THE SURFACE OF A PHOTOCONDUCTIVE INSULATING LAYER, THEN EXPOSING THE PHOTOCONDUCTIVE INSULATING LAYER TO AN IMAGE PATTERN OF LIGHT AND SHADOW TO BE REPRODUCED AND PLACING THE TRANSFER MEMBER IN CONTACT WITH THE CHARGED DEVELOPER POWDER TO TRANSFER A POWDER IMAGE TO SAID TRANSFER MEMBER, SAID TRANSFER MEMBER BEING CHARACTERIZED BY ITS ABILITY TO LATERALLY CONDUCT ELECTRICITY. 